Many people who are profoundly deaf have sensorineural hearing loss. This type of hearing loss can arise from the absence or the destruction of the hair cells in the cochlea that no longer transduce acoustic signals into auditory nerve impulses. Individuals with sensorineural hearing loss may be unable to derive significant benefit from hearing aid systems alone, no matter how loud the acoustic stimulus. This is because the natural mechanism for transducing sound energy into auditory nerve impulses has been damaged. Thus, in the absence of properly functioning hair cells, auditory nerve impulses cannot be generated directly from sounds.
To overcome sensorineural deafness, cochlear implant (CI) systems, or cochlear prostheses, have been developed that can bypass the hair cells located in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers. This leads to the perception of sound in the brain and provides at least partial restoration of hearing function. Most of these cochlear prosthesis systems treat sensorineural deficit by stimulating the ganglion cells in the cochlea directly using an implanted electrode or lead that has an electrode array. Thus, a cochlear prosthesis operates by directly stimulating the auditory nerve cells, bypassing the defective cochlear hair cells that normally transduce acoustic energy into electrical activity in the connected auditory nerve cells.
External components of a CI system are removably coupled to the internal components of the CI system. Specifically, both the external components and the internal components include magnets. These magnets maintain a transmitter of the external components and an antenna of the internal components in position such that the transmitter and the antenna can communicate via electromagnetic transmission or optical transmission, among others, through the skin of the user. The internal magnet is held within a CI in the center of the antenna coil. When subjected to certain forces, such as impact forces from a fall or impact against hard object, or in the presence of a strong magnetic field during a magnetic resonance imaging (MRI) procedure, this internal magnet can dislodge from the CI or from portions of the CI, or can flip.
For example, an MRI device uses powerful magnetic fields to produce detailed images of internal structures of the human body, and is often used to image the head of a patient. If a user of a CI system were exposed to the magnetic fields produced by an MRI device, the magnet within the CI could dislodge from its original position, move within the body of the user, or flip due to the drastic and powerful change in the magnetic fields surrounding the CI.
In some cases, particularly when a relatively large magnetic field strength is used, a user of a CI system may need to undergo minor surgery to remove the magnet prior to an MRI procedure, and then endure a second surgery to reinstall the magnet after the MRI. These surgeries to remove and reinstall the magnet pose a risk of damage to the implant. These surgeries also require general anesthetic when performed on children, and subject the patient to risk of infection and breakdown of the skin overlying the CI due to the repeated surgeries.
Additional reasons to remove the magnet include preventing demagnetization of the internal magnet during MRI, replacing a magnet that has been demagnetized from one or more MRI procedures, replacing a magnet that has been otherwise damaged or dislodged, and eliminating artifacts on the MRI image caused by the internal magnet.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.